Medical doctors regularly prescribe drugs to be taken by injection or in oral format, whether it is to be taken in a hospital or outside of the hospital. The preparation of these prescriptions by pharmacists often includes the filling, or pre-filling, of containers to contain these drugs. Such containers may include syringes, cassettes, bags, vials, etc. It is thus often critical for pharmacists to ensure that the filling of the containers be performed with great accuracy. It is also important that the filling of the containers be performed safely and with minimal risk of contamination.
The process of filling syringes has revealed a number of technical problems. Due to the physical manufacturing imperfections of the syringe cylinder as well as the friction of the plunger's seal, significant variations in back pressure result during the filling process. These variations can affect and vary the total volume transferred to the syringe.
Health and safety regulations also prohibit any volumetric discrepancies of more than 10% for any oral drugs substance and only 2% for narcotic substances. In that several syringes are typically filled with a given dose of drug, it is critical that the transfer of liquid be performed rapidly and with high accuracy.
Traditionally, and still recently, peristaltic pumps have been employed in medical applications for their unique ability to force liquid through tubes without direct contact. Non-limitative examples of filling apparatuses using peristaltic pumps are shown in U.S. Pat. Nos. 3,662,517; 6,976,349 and 7,703,483.
However, with increased back pressure, the flexible tubing can lead to both errors in accuracy as well as substantial residual pressure causing spillage as the filled syringes are removed.
One way to overcome the problem of back pressure is to use an intermediate pumping syringe between the bulk source of drug and the receiving syringe to be filled.
This solution has been proposed in U.S. Pat. Nos. 3,935,883; 4,187,890 and 5,911,252.
However, the apparatuses disclosed in U.S. Pat. Nos. 3,935,883 and 4,187,890 use a motor-driven mechanical crank to actuate the plunger of the pumping syringe. Such a mechanical assembly does not provide the level of accuracy required by health and safety regulations. Moreover, these apparatuses do not provide for calibration.
U.S. Pat. No. 5,911,252 does propose a more advanced apparatus. But again, the precise actuation of the plunger of the pumping syringe is not addressed and the level of accuracy required by health and safety regulations is likely not complied with.
Hence, there is a need for a novel apparatus for filling syringes and other drug containers, as well as novel methods relating thereto, which mitigates at least some shortcomings of the prior art.